Previously, many granular products and some liquids have been shipped and stored in large bulk bags which may contain as much as a ton or more of material. Some of these bulk bags are flexible and when empty can be folded to a generally flat condition. One such flexible bag is disclosed and claimed in U.S. Pat. No. 5,104,236.
These flexible bags have generally rectangular ends interconnected by generally rectangular side walls and, when filled, can be stacked one on top of another. For some applications the bags are made of a woven fabric and for other applications a plastic material. For some applications, and particularly for storing liquids or hazardous materials, a bag of a water impervious plastic material is received in and reinforced and protected by a bag of a woven fabric. Usually, these bags have a spout in one or both ends for filling and emptying the bags. Further, for some applications, it is desirable to have a bag of a water impervious plastic material encasing a bag of woven fabric to protect the contents of the inner bag and to contain the contents of the inner bag that leak through the inner bag.
Typically these bags are produced by severing a tubular blank to form triangular portions adjacent opposite ends of the blank. Adjacent sides of adjacent triangular portions are then connected together such as by stitching or heat sealing the edges together to form generally square and spaced apart top and bottom walls of the bag. The connections between adjacent triangular portions of the top and bottom walls of the bags are typically weaker than seamless portions of the bag and are hence subject to rupturing or tearing especially during moving or shipping of filled bags. Further, especially when liquids are being carried by the bulk bag, high stresses can result in the top and bottom of the bags, both when the bags are being lifted such as for loading onto a vehicle for shipping, and also during shipping due to the shifting of the liquid within the bag during shipping.
Thus, current bags have the weakest portion of the bag, where the triangular portions are connected together, in the top and bottom walls of the bag which can experience the highest stresses during use of the bag. Therefore, the bags are subject to rupturing adjacent their top and bottom walls which limits the load bearing capacity of the bags.